There are hundreds of applications where there is a need of spray systems to apply or use the liquid efficiently. Many industrial applications require high volumes of liquids to be emulsified, dispersed, homogenized, and degassed while in the process line. This can be accomplished through use of atomizers. Atomization refers to the conversion of bulk liquid into a spray or mist (i.e. collection of drops), often by passing the liquid through a nozzle.
There are several types of spray nozzles known in the art, categorized based on the energy input used. The hydraulic spray nozzles use the liquid pressure as the energy source to break the liquid into droplets. With the increase of the fluid pressure, the flow also increases and the size of the fluid drop decreases. The gas atomized spray nozzles utilize a gaseous source to break the liquid to the droplets. The atomization is achieved by either breaking the liquid into droplets by using only gas, or by causing the liquid to come into contact with a surface to break the liquid stream and then mixing the air into it to atomize the liquid. External mixing nozzles mix fluids outside the nozzle. Sometimes a gas used to atomize a liquid may also react with the liquid, which in turn can cause damage the inside of the nozzle. Thus, this type of nozzle may prevent such damage to the nozzle by allowing mixing and atomization of liquid outside the nozzle.
Unlike these conventional atomizing nozzles that rely on pressure and high-velocity motion to shear a fluid into small drops, an ultrasonic atomizer uses only low ultrasonic vibration energy to break up water or any other liquid into small particles of a size from a few microns to hundreds of microns. A typical ultrasonic atomizer consists of an ultrasonic transducer for ultrasound generation, a reservoir for a liquid that is to be atomized and an ejection nozzle, also called a horn. A power supply supplies electrical energy to the transducer and causes it to oscillate at a certain ultrasonic frequency. This electrical oscillation passes to some type of converter, such as piezoelectric material, and is then converted into mechanical vibrations in the ultrasonic range. The resulting intensive mechanical vibrations produce a field of waves on the surface of a liquid, causing the velocity of the liquid particles in the waves to become so high that it overcomes the effects of gravity and surface tension forces and causes small particles to detach from the liquid surface into the air.
The size of the droplets produced by the ultrasound atomizer depends on properties of a liquid and on a particular ultrasound frequency used in the ultrasonic oscillator. The atomizing capacity of the ultrasound atomizer will typically depend on the size of the oscillating material that converts the electric vibrations into mechanical vibrations. The larger the size of the piezoelectric elements, the greater is the water atomizing capacity. The magnitude of the electrical power supplied to the ultrasound atomizer also effects to atomizing capacity.
One of the problems associated with conventional atomizers is that they generally use only a single spray-nozzle or probe and thus can only process one liquid sample at a time. The inability to increase the mass output from such single-probe atomizers presents a major challenge in industrial applications where large quantities of particles need to be delivered. Another drawback of conventional single-probe atomizers is that they require more labor because each sample of liquid has to be processed separately.
Attempts have been made to solve the problems associated with conventional atomizers by providing atomization systems that utilize multiple nozzles in attempt to increase the efficiency of such systems.
For example, U.S. Pat. No. 6,764,720 to Pui et al. describes an electrospray dispensing device comprising multiple nozzle structures for producing multiple sprays of particles. The sprays of particles are produced by creating a non-uniform electrical field between the nozzle structures and an electrode that is electrically isolated from the structures.
U.S. Pat. No. 4,845,517 to Temple et al. is directed to an ink jet “drop-on-demand” printer that has a number of parallel channels each containing ink. A mercury thread extends through each channel and is connected to electrical current flow. The current flow causes electromagnetic deformation of the mercury thread, which leads to a pressure pulse in the ink causing ejection of an ink droplet from a chosen channel.
U.S. Pat. No. 4,074,277 to Lane et al. discloses an ink jet synchronization scheme having multi-nozzle ink jet array, wherein the drop formation in each nozzle is synchronized acoustically by individual acoustic fiber input to each of the nozzles.
U.S. Pat. No. 4,742,810 to Anders et al. discloses an ultrasonic atomizer system designed to atomize and inject fuel into internal combustion engines. The system includes a housing with a pressure chamber, an ultrasonic vibrator that protrudes into the housing, and transport lines that transmit vibrations from pressure chamber to nozzles, from which the streams of fuel are ejected.
While the above described systems may have some advantages over the previously known systems, they are directed to different types of atomization systems having different applications than the ultrasonic atomizer of the present invention. For example, these prior art systems do not produce a low velocity mist as a result of atomization. Additionally, the above systems have somewhat complex structures, and are not designed for atomizing large quantities of liquids with reduced electric power consumption.
What is desired, therefore, is an improved ultrasonic atomizer probe that addresses tedious labor-intensive tasks required by conventional atomizing probes. It is further desired to provide an atomizing probe that maximizes productivity and efficiency at the lowest possible power supply.